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Showing papers on "Ferric published in 1997"


Journal ArticleDOI
TL;DR: In this article, the 1s → 3d pre-edge features of high-spin ferrous and ferric model complexes in octahedral, tetrahedral, and square pyramidal environments were investigated and the allowable many-electron excited states were determined using ligand field theory.
Abstract: X-ray absorption Fe−K edge data on ferrous and ferric model complexes have been studied to establish a detailed understanding of the 1s → 3d pre-edge feature and its sensitivity to the electronic structure of the iron site. The energy position and splitting, and intensity distribution, of the pre-edge feature were found to vary systematically with spin state, oxidation state, geometry, and bridging ligation (for binuclear complexes). A methodology for interpreting the energy splitting and intensity distribution of the 1s → 3d pre-edge features was developed for high-spin ferrous and ferric complexes in octahedral, tetrahedral, and square pyramidal environments and low-spin ferrous and ferric complexes in octahedral environments. In each case, the allowable many-electron excited states were determined using ligand field theory. The energies of the excited states were calculated and compared to the energy splitting in the 1s → 3d pre-edge features. The relative intensities of electric quadrupole transitions...

1,181 citations


Journal ArticleDOI
TL;DR: A review of information related to low molecular weight metal chelators isolated from wood decay fungi is presented in this paper, where the presence of the chelator in wood degraded by G. trabeum has been demonstrated by ELISA and TEM immunolabelling studies.

419 citations


Journal ArticleDOI
TL;DR: In this article, the efficiency of arsenic removal from source waters and artificial freshwaters during coagulation with ferric chloride and alum was examined in bench-scale studies, and the results showed that the removal of arsenic(III) was less efficient and more strongly influenced by source water composition.
Abstract: The efficiency of arsenic removal from source waters and artificial freshwaters during coagulation with ferric chloride and alum was examined in bench-scale studies. Arsenic(V) removal by either ferric chloride or alum was relatively insensitive to variations in source water composition below pH 8. At pH 8 and 9, the efficiency of arsenic(V) removal by ferric chloride was decreased in the presence of natural organic matter. The pH range for arsenic(V) removal with alum was more restricted than with ferric chloride. For source waters spiked with 20 μg/L arsenic(V), final dissolved arsenic(V) concentrations in the product water of less than 2 μg/L were achieved with both coagulants at neutral pH. Removal of arsenic(III) from source waters by ferric chloride was both less efficient and more strongly influenced by source water composition than removal of arsenic(V). The presence of sulfate (at pH 4 and 5) and natural organic matter (at pH 4 through 9) adversely affected the efficiency of arsenic(III) removal by ferric chloride. Arsenic(III) could not be removed from source waters by coagulation with alum.

368 citations


Journal ArticleDOI
TL;DR: Changes between iron redox states (ferrous or ferric) drive numerous reactions involving electron transfer that are important for plants, highlighting new mechanisms in plant adaptative responses.

303 citations


Journal ArticleDOI
TL;DR: Comparison of [Fe(III)(PY5)(OMe)](OTf)(2) to other coordination complexes capable of hydrogen atom abstraction shows that, although a strong correlation exists between the thermodynamic driving force of reaction and the rate of reaction, other factors appear to further modulate the reactivity.
Abstract: Lipoxygenases are mononuclear non-heme iron enzymes that regio- and stereospecifcally convert 1,4-pentadiene subunit-containing fatty acids into alkyl peroxides. The rate-determining step is generally accepted to be hydrogen atom abstraction from the pentadiene subunit of the substrate by an active ferric hydroxide species to give a ferrous water species and an organic radical. Reported here are the synthesis and characterization of a ferric model complex, [FeIII(PY5)(OMe)](OTf)2, that reacts with organic substrates in a manner similar to the proposed enzymatic mechanism. The ligand PY5 (2,6-bis(bis(2-pyridyl)methoxymethane)pyridine) was developed to simulate the histidine-dominated coordination sphere of mammalian lipoxygenases. The overall monoanionic coordination provided by the endogenous ligands of lipoxygenase confers a strong Lewis acidic character to the active ferric site with an accordingly positive reduction potential. Incorporation of ferrous iron into PY5 and subsequent oxidation yields a sta...

261 citations


Journal ArticleDOI
TL;DR: In this paper, the Mossbauer and Raman spectroscopies were used to identify green rust as a mineral in a reductomorphic soil from samples extracted in the forest of Fougeres (Brittany-France).

249 citations


Journal ArticleDOI
TL;DR: Structures of nitric oxide reductase (NOR) in the ferric resting and the ferrous CO states have been solved at 2.0 Å resolution and provide significant new insights into how NO is reduced in biological systems.
Abstract: Structures of nitric oxide reductase (NOR) in the ferric resting and the ferrous CO states have been solved at 2.0 A resolution. These structures provide significant new insights into how NO is reduced in biological systems. The haem distal pocket is open to solvent, implicating this region as a possible NADH binding site. In combination with mutagenesis results, a hydrogen-bonding network from the water molecule adjacent to the iron ligand to the protein surface of the distal pocket through the hydroxyl group of Ser 286 and the carboxyl group of Asp 393 can be assigned to a pathway for proton delivery during the NO reduction reaction.

178 citations


Journal ArticleDOI
TL;DR: Overall, the kinetics of ferric P450 reduction cannot be generalized among different P450s in various systems, and concepts regarding influence of substrate, reaction sequence, and a rate-limiting step are not very universal.
Abstract: The reduction of ferric cytochrome P450 (P450) to ferrous is the first chemical step in almost all P450 reactions, and many characteristics of this step have been reported. Reduction kinetics of rabbit and human P450s were measured in a variety of systems. As reported earlier, P450 reduction is biphasic in microsomes and some purified P450 systems. However, this is not an inherent property of P450s, and some low- and high-spin iron P450s were reduced with single-exponential kinetics. Contrary to a generalized view, the presence of substrate is not necessary for rapid reduction of all P450s. Also, low-spin heme can be reduced as rapidly as high-spin in several P450s. P450s varied considerably in their reduction behavior, and even a single P450 showed remarkably different reduction kinetics when placed in various environments. P450 3A4 reduction was examined in liver microsomes, a reconstituted system, a fusion protein in which it was linked to NADPH−P450 reductase, and baculovirus and bacterial membranes i...

173 citations


Journal ArticleDOI
Xuan Zhang1, Qin Chen1, Dean C. Duncan1, Rene J. Lachicotte1, Craig L. Hill1 
TL;DR: A tetranuclear ferric Keggin sandwich-type heteropolyanion has been synthesized by the reaction of the lacunary species Δ-Na8H[PW9O34] with FeCl2 followed by O2 oxidation in nonaqueous media.
Abstract: A tetranuclear ferric Keggin sandwich-type heteropolyanion has been synthesized by the reaction of the lacunary species Δ-Na8H[PW9O34] with FeCl2 followed by O2 oxidation in nonaqueous media. The structure of [(n-C4H9)4N]6[FeIII4(H2O)2(PW9O34)2]·4CH3CN·2CH2Cl2·2H2O (TBA-1) was determined by single-crystal X-ray diffraction (orthorhombic, Pbca; R = 0.0693 for 14 963 reflections with Fo > 4σ(Fo)). The compound was further characterized by infrared and UV−visible spectroscopy, electrochemistry, magnetic susceptibility, FAB mass spectrometry (FAB-MS), and elemental analyses. Five lines of evidence are consistent with the FeIII4 oxidation state: (i) valence sum calculations from the X-ray structure (ca. 2.86 ± 0.07 per Fe); (ii) the rest potential from cyclic voltammetry; (iii) charge balance requirements; (iv) titration with CeIV(SO4)2; and (v) oxidation by O2. In contrast to the tetranuclear ferric Wells−Dawson-derived sandwich complex, [FeIII4(H2O)2(P2W15O56)2]12-, TBA-1 can only be prepared from a ferrous...

151 citations


Journal ArticleDOI
TL;DR: The spectral and kinetic properties of the intermediate identify it as the FeIIO2 complex of nNOSoxy, which may be important regarding the role of this cofactor in NO synthesis.

149 citations


Journal ArticleDOI
TL;DR: The analysis of steady-state kinetic measurements of the NO reductase activity shows a sigmoidal relation between rate of NO reduction and NO concentration, consistent with a model describing sequential binding of two molecules of NO to the reduced enzyme.

Journal ArticleDOI
TL;DR: In this article, the degradation of compressed polypyrrole powder, with FeCl 4 − as a dopant, at 90 °C has been monitored by IR spectra and evolved gas analysis (EGA), showing a decrease in the absorption of the electronic transition band, reduction in intensity and slight shift in position of most of the IR absorptions.

Journal ArticleDOI
TL;DR: It is proposed that the information flux from the cell surface to the cytoplasm involves a series of conformational changes of the proteins FecA, FecR, and FecI in that order that determines the degree of the response of the cell to ferric citrate in the medium.
Abstract: Transcription of the ferric citrate transport genes of Escherichia coli is induced by a novel mechanism. Ferric citrate, the inducer, does not have to enter the cytoplasm to initiate transcription. Interaction of ferric citrate with the outer membrane receptor protein FecA induces transcription of the fec transport gene operon consisting of the fecIRABCDE genes. A signal from FecA occupied with ferric citrate is transmitted across the outer membrane into the periplasm with the help of the electrochemical potential of the cytoplasmic membrane and the Ton system. The signal is then transduced across the cytoplasmic membrane by the FecR protein, which in turn activates the FecI σ-factor that directs the RNA polymerase core-enzyme to the fec transport gene promoter. The promoter of the regulatory genes fecI and fecR is not controlled by ferric citrate but is regulated by iron via the Fur repressor. It is proposed that the information flux from the cell surface to the cytoplasm involves a series of conformational changes of the proteins FecA, FecR, and FecI in that order. The level of the regulatory proteins FecI and FecR is adjusted to the intracellular iron concentration and determines the degree of the response of the cell to ferric citrate in the medium. Ferric citrate induces transcription of the fec transport genes under iron-limiting conditions. A regulatory device similar to the ferric citrate transport system exists in Pseudomonas putida WCS358. The synthesis of the outer membrane receptor PupB, involved in the transport of the ferric pseudobactins BN7 and BN8, is induced by the ferric siderophores and requires PupB and two proteins homologous to FecI and FecR.

Journal ArticleDOI
TL;DR: Hydrogen peroxide proved as effective as linoleic acid hydroperoxide in inducing dopamine oxidation and conversion to 6-hydroxydopamine quinone, consistent with a hydroxyl radical independent hydroxyation/oxidation mechanism basically different from the Fenton reaction.
Abstract: Exposure of dopamine to an excess of linoleic acid 13-hydroperoxide (13-hydroperoxyoctadecadienoic acid) in the presence of ferrous ions in Tris buffer, pH 7.4, resulted in a relatively fast, oxygen-independent reaction exhibiting first-order kinetics with respect to both catecholamine and metal concentrations. Product analysis in the early stages revealed the presence of significant amounts of the quinone of the neurotoxin 6-hydroxydopamine, together with some aminochrome and ill-defined melanin-like material. Quinone formation required the presence of iron, either in the ferrous or ferric form, and was unaffected by peroxidase, catalase, and hydroxyl radical scavengers, e.g. mannitol, as well as biologically relevant antioxidants, like ascorbate and glutathione. Hydrogen peroxide proved as effective as linoleic acid hydroperoxide in inducing dopamine oxidation and conversion to 6-hydroxydopamine quinone. Metal chelators, including EDTA and bipyridyl, markedly suppressed quinone formation without, however, inhibiting dopamine oxidation. These and other results are consistent with a hydroxyl radical independent hydroxylation/oxidation mechanism basically different from the Fenton reaction, which involves direct interaction of the peroxide with a dopamine-Fe(III) chelate generated during the process.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the Fenton system's ability to oxidize dichlorvos with Fenton's reagent in solutions containing various ions, and showed that the added amount of ferrous ions, the higher the elimination rate of dichlor vos and the oxidization rate after the addition of ferric ions is far smaller than that of adding ferrous ion.

Journal Article
TL;DR: Iron overload results in iron toxicity, mainly due to the formation of hydroxyl radicals that strongly react with all kinds of biomolecules, of which DNA damage has the most deleterious consequences.
Abstract: Under oxic conditions and at pH 7, ferric iron is insoluble, and complex formation of Fe3+ with ligands is required to supply cells with iron. Bacteria and fungi synthesize and secrete low-molecular-weight compounds, termed siderophores, that bind Fe3+. Certain human pathogens take up iron from human transferrin, lactoferrin, hemoglobin, and heme. The ferric siderophores are actively transported into bacterial cells by highly specific transport systems. In Gram-negative bacteria, the ferric siderophores and iron released from the host proteins are actively transported across the outer membrane (OM). The electrochemical potential of the cytoplasmic membrane (CM) energizes transport across the outer membrane, which requires an energy-transducing device, consisting of the proteins TonB, ExbB and ExbD, from the CM to the OM. Active transport across the CM is energized by ATP hydrolysis. Transport is regulated at the level of gene transcription. In Gram-negative bacteria, this is controlled by the Fur protein, in most gram-positive bacteria, by the DtxR protein. Fur and DtxR act as repressors when loaded with Fe2+. In the cytoplasm, iron is released from the siderophores by reduction to Fe2+, and the siderophores are either inactivated or secreted. The intracellular iron is built into heme and non-heme iron proteins, and a small proportion is incorporated into bacterioferritin, but most of the iron is present in a poorly defined state. Iron overload results in iron toxicity, mainly due to the formation of hydroxyl radicals that strongly react with all kinds of biomolecules, of which DNA damage has the most deleterious consequences.

Journal ArticleDOI
TL;DR: It is suggested that copper ions bind to albumin and induce site-specific degradation by HO generated at the copper-binding site, whereas the Fe2+/EDTA-catalyzed oxidation system induces non- specific degradation of albumin byHO generated by the Fenton reaction between H2O2 and free Fe2-/ EDTA in solution.

Journal ArticleDOI
TL;DR: In this paper, the competition between SO42− and CO32− was studied by oxidising Fe(OH)2 in the simultaneous presence of both anions, and it was shown that GR1(CO32−) forms preferentially and GR2(SO42−) is clearly observed only when the amount of carbonate anions is not sufficient to transform all the initial ferrous hydroxide.

Journal ArticleDOI
TL;DR: Hydroxyl radical production was found to be enhanced significantly by reduced glutathione, cysteine, ascorbic acid, and selected catechols, but not by mannitol, melatonin or tyramine, and the augmented effects were linearly proportional to the amount of added reductant.

Journal ArticleDOI
TL;DR: In this article, it was found that several chalcopyrite samples were more effectively leached in ferrous sulfate solution than in ferric sulfate, and the amount of extracted copper increased markedly with increasing ferrous oxide addition and decreasing pH.

Journal ArticleDOI
TL;DR: The results indicate that glutathione requires digestion to Cys or Cys-Gly in order to promote iron uptake, and cysteine and reduced cysteinyl glycine are capable of enhancing iron uptake from soluble and insoluble ferric iron.
Abstract: Human and animal studies have shown that amino acids and peptides influence iron absorption from the intestinal lumen. This study was conducted using Caco-2 cell monolayers as the experimental model to determine whether similar effects on iron absorption occur. Conditions were chosen to mimic the pH of the intestinal lumen and the most likely order whereby ferric and ferrous forms of iron would combine with various amino acids and dipeptides resulting from protein digestion. We demonstrated the enhancing effect of cysteine and reduced cysteinyl glycine on iron uptake by Caco-2 cells. The addition of glutathione to the transport media had no effect on uptake from ferrous or ferric iron complexes, nor did it affect iron solubility. Cysteine and reduced cysteinyl glycine increased iron solubility when added to a solution containing insoluble iron. This effect is different from that of ascorbate, which must be combined with soluble ferric iron at pH 2 to reduce and solubilize iron. Taken together, these observations are evidence that cysteine and reduced N-terminal cysteine peptides are capable of enhancing iron uptake from soluble and insoluble ferric iron. These results qualitatively reflect those observed in human studies. Our results indicate that glutathione requires digestion to Cys or Cys-Gly in order to promote iron uptake. The similarity between this study and human studies further reinforces that the Caco-2 cell model is a useful tool in studies of iron absorption and bioavailability.

Journal ArticleDOI
TL;DR: In this paper, a study of the recovery of copper, cobalt, nickel and zinc from copper converter slag by roasting with ferric sulphate was carried out in order to bring the metal values into solution.

Journal ArticleDOI
15 Jun 1997-Yeast
TL;DR: It is demonstrated that AFT1 protein is required for maintaining detectable non‐induced levels of FET3 expression and for induction of FRE2 in iron starvation conditions, and it might link induction of genes for iron uptake to other metabolically dominant requirements for cell growth.
Abstract: High-affinity iron uptake in Saccharomyces cerevisiae involves the extracytoplasmic reduction of ferric ions by FRE1 and FRE2 reductases. Ferrous ions are then transported across the plasma membrane through the FET3 oxidase-FTR1 permease complex. Expression of the high-affinity iron uptake genes is induced upon iron deprivation. We demonstrate that AFT1 is differentially involved in such regulation. Aft1 protein is required for maintaining detectable non-induced level of FET3 expression and for induction of FRE2 in iron starvation conditions. On the contrary, FRE1 mRNA induction is normal in the absence of Aft1, although the existence of AFT1 point mutations causing constitutive expression of FRE1 (Yamaguchi-Iwai et al., EMBO J. 14: 1231-1239, 1995) indicates that Aft1 may also participate in FRE1 expression in a dispensable way. The alterations in the basal levels of expression of the high-affinity iron uptake genes may explain why the AFT1 mutant is unable to grow on respirable carbon sources. Overexpression of AFT1 leads to growth arrest of the G1 stage of the cell cycle. Aft1 is a transcriptional activator that would be part of the different transcriptional complexes interacting with the promoter of the high-affinity iron uptake genes. Aft1 displays phosphorylation modifications depending on the growth stage of the cells, and it might link induction of genes for iron uptake to other metabolically dominant requirement for cell growth.

Journal ArticleDOI
TL;DR: This work studied the ligand-bound and photoproduct states involved in the interaction of NO with the heme iron and the distal pocket of the protein, finding that ferric nitrosyl myoglobin has a lower photopProduct yield than the mutant, MbIII(H64L)NO, where thedistal histidine is replaced by leucine.
Abstract: Hemeproteins play an important role in the signaling processes mediated by nitric oxide (NO). For example, the production of NO by nitric oxide synthase, the activation of guanylate cyclase by binding NO, and the scavenging of NO by hemoglobin, myoglobin, and cytochrome c oxidase all occur through unique mechanisms of interaction between NO and hemeproteins. Unlike carbon monoxide (CO) and oxygen (O2), which have been studied extensively, the reactions of NO with ferric and ferrous hemeproteins are not as well characterized. In this work, NO binding to myoglobin is studied using cryogenic optical spectroscopy and Fourier transform infrared spectroscopy (FTIR) in order to characterize the ligand-bound and photoproduct states involved in the interaction of NO with the heme iron and the distal pocket of the protein. For ferrous nitrosyl myoglobin (MbIINO), optical spectroscopy is used to show that the ligand-bound state can be converted to >95% stable photoproduct below 10 K. The Soret peak of the photoproduct is red-shifted by 4 nm relative to deoxy-myoglobin (Mb), similar to previous results for carbonmonoxy- (MbCO) and oxy-myoglobin (MbO2) (Miller et al., 1996). MbIINO completely rebinds by 35 K, indicating that the rebinding barrier for NO is lower than MbCO, consistent with room temperature picosecond kinetic measurements. For ferric nitrosyl myoglobin (MbIIINO), we find that the photoproduct yield at cryogenic temperatures is less than unity and dependent on the distal pocket residue. Native MbIIINO has a lower photoproduct yield than the mutant, MbIII(H64L)NO, where the distal histidine is replaced by leucine. The rebinding rates for the native and mutant species are similar to each other and to MbIINO. By using FTIR difference spectroscopy (photolyzed/unphotolyzed) of isotopically labeled ferrous nitrosyl myoglobin (MbIINO), the NO stretching frequencies in both the ligand-bound states and photoproduct states are determined. Two ligand-bound conformational states (1607 and 1613 cm-1) and two photoproduct conformational states (1852 and 1857 cm-1) are observed for MbIINO. This is the first direct observation of photolyzed NO in the distal pocket of myoglobin. The ligand-bound frequencies are consistent with a bent MbIINO moiety, where the unpaired pi*(NO) electron remains localized on NO, causing nu(N-O) to be approximately 300 cm-1 lower than MbIIINO. Similar to MbO2, we suggest that Nepsilon of the distal histidine is protonated, forming a hydrogen bond to the NO ligand. For native MbIIINO, a single ligand-bound conformational state with respect to nu(N-O) is observed at 1927 cm-1. This frequency decreases to 1904 cm-1 for the mutant, MbIII(H64L)NO, contrary to the increase of the carbon monoxide (CO) stretching frequency in the isoelectronic MbII(H64L)CO mutant versus native MbCO. For linear MbIIINO, we suggest that backbonding from the unpaired pi*(NO) electron to iron results in an increased positive charge on the NO ligand, Fe(delta-)-NO(delta+). This can be facilitated by tautomerism of the distal histidine, leaving Nepsilon of the imidazole ring unprotonated and able to accept positive charge from the Fe(delta-)-NO(delta+) moiety, resulting in a higher bond order (and a 23 cm-1 shift to higher frequency) for native MbIIINO versus MbIII(H64L)NO, where this interaction is absent. These different interactions between the distal histidine and the ferrous versus ferric species illustrate potential ways the protein can stabilize the bound ligand and demonstrate the versatile nature by which NO can bind to hemeproteins.

Journal ArticleDOI
TL;DR: In this paper, the effect of temperature, oxalate concentration and pH on hematite dissolution was studied under various experimental conditions, and it was found that the dissolution process is much faster in an inert atmosphere under visible light.

Journal ArticleDOI
TL;DR: The kinetics of the catalytic cycle and irreversible inactivation of horseradish peroxidase C (HRP-C) reacting with m-chloroperoxybenzoic acid (mCPBA) have been studied and the importance of single turnover experiments is demonstrated.

Journal ArticleDOI
TL;DR: In this paper, the precipitation of hematite from ferric chloride media was systematically investigated in a series of autoclave experiments and it was shown that the filterability of the fine precipitated hematites is greatly improved by the presence of hemetite seed.

Journal ArticleDOI
TL;DR: Oligonucleotide-directed mutagenesis has been used to replace arginine-47 with glutamate in cytochrome P-450 BM3 from Bacillus megaterium and in its haem domain, and the results are discussed in the light of the three-dimensional structure of the enzyme.
Abstract: Oligonucleotide-directed mutagenesis has been used to replace arginine-47 with glutamate in cytochrome P-450 BM3 from Bacillus megaterium and in its haem domain. The mutant has been characterized by sequencing, mass spectrometry, steady-state kinetics and by optical and NMR measurements of substrate binding. The mutant retains significant catalytic activity towards C12-C16 fatty acids, catalysing hydroxylation in the same (omega-1, omega-2, omega-3) positions with kcat/Km values a factor of 14-21 lower. C12-C16 alkyl trimethylammonium compounds are relatively poor substrates for the wild-type enzyme, but are efficiently hydroxylated by the arginine-47-->glutamate mutant at the omega-1, omega-2 and omega-3 positions, with kcat values of up to 19 s-1. Optical spectroscopy shows that the binding of the C14 and C16 alkyl trimethylammonium compounds to the mutant is similar to that of the corresponding fatty acids to the wild-type enzyme. Paramagnetic relaxation measurements show that laurate binds to the ferric state of the mutant in a significantly different position, 1.5 A closer to the iron, than seen in the wild-type, although this difference is much smaller ( approximately 0.2 A) in the ferrous state of the complex. The binding of a substrate having the same charge as residue 47 to the ferric state of the enzyme is roughly ten times weaker than that of a substrate having the opposite charge (and thus is able to make an ion-pair interaction with this residue). The results are discussed in the light of the three-dimensional structure of the enzyme.

Journal ArticleDOI
TL;DR: Analysis of the results from the batch culture indicates that the initial number of bacteria that are adapted to the solution depends on the concentrations of ferrous and arsenite ions, and an experiment designed to obtain kinetic data under these conditions is reported.
Abstract: The concentrations of ferrous and ferric ions change dramatically during the course of the batch experiments usually performed to study the kinetics of the bacterial oxidation of ferrous ions and sulfide minerals. This change in concentration of the iron species during the course of the experiment often makes it difficult to interpret the results of these experiments, as is evidenced by the lack of consensus concerning the mechanism of bacterial leaching. If the concentrations of ferrous and ferric ions were constant throughout the course of the batch experiment, then the role of the bacteria could be easily established, because the rate of the chemical leaching should be the same at a given redox potential in the presence and in the absence of bacteria. In this paper we report an experiment designed to obtain kinetic data under these conditions. The redox potential is used as a measure of the concentrations of ferrous and ferric ions, and the redox potential of the leaching solution is controlled throughout the experiment by electrolysis. The effects of ferrous, ferric, and arsenite ions on the rate of growth of Thiobacillus ferrooxidans on ferrous ions in this redox-controlled reactor are presented. In addition, the growth of this bacterium on ferrous ions in batch culture was also determined, and it is shown that the parameters obtained from the batch culture and the redox-controlled batch culture are the same. An analysis of the results from the batch culture indicates that the initial number of bacteria that are adapted to the solution depends on the concentrations of ferrous and arsenite ions.

Journal ArticleDOI
TL;DR: Putrebactin was determined to be 1,11-dihydroxy-1,6,11,16-tetraazacycloeicosane-2,5,12,15-tetrone, by 1H and 13C NMR spectroscopy, fast atom bombardment and chemical ionization mass spectrometry, and X-ray crystallography.
Abstract: Shewanella putrefaciens is a bacterium implicated in oil pipeline corrosion and fish spoilage, and is one of very few isolated microorganisms able to use iron(III) as an electron acceptor. S. putrefaciens strain 200 produced a novel cyclic dihydroxamate siderophore, putrebactin, during aerobic growth. Putrebactin was determined to be 1,11-dihydroxy-1,6,11,16-tetraazacycloeicosane-2,5,12,15-tetrone, a cyclic dimer of succinyl-(N-hydroxyputrescine), by 1H and 13C NMR spectroscopy, fast atom bombardment and chemical ionization mass spectrometry, and X-ray crystallography. The protonation constants of putrebactin were determined to be 8.82 and 9.71. Potentiometric titration of the ferric complex revealed a sharp equivalence point at 3.0 equivalents of base per mole of Fe(III), consistent with loss of 3 protons per equivalent of bound ferric ion, while Job's method of continuous variation supported a shift from 1 : 1 to 3 : 2 complex stoichiometry as a function of pH. Putrebactin is similar in structure to two other siderophores, bisucaberin and alcaligin, produced by unrelated bacteria.